Immature mouse follicles are isolated and grown in culture for nine days and then biosynthetically labeled with radioactive amino acids or sugars. During this maturation period the zona pelluuda, an acellular matrix comprised of glycoproteins is formed around oocytes. The proteins of the oocyte and zona pellucida can be displayed on two dimensional O'Farrell gels and followed for changes during this period of oocyte development. Methods are being developed to isolate the zona pellucida from the oocyte and determine its protein composition. These proteins are thought to mediate the specie-specific sperm-egg interaction by acting as recognition markers and subsequent sperm binding sites. We hope to identify and characterize these proteins both as to their physical properties and site of syntheisis.